phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('4b70af7242b73d11adfbc110c9d4f7c4', -1, 1513306043, 1513306043, '365acf4b', 8, 0, 0)

Line : 189
File : sessions.php